The research outlined in this proposal is designed to provide new information about neuronal organization which underlies the production of movements directed toward external stimuli. In the frog, apparently identical prey orienting movements can be triggered either visually or tactually, suggesting that visual and tactile signals converge somewhere on or prior to the circuitry responsible for generating the motoneuron discharge patterns which underly orienting movements. Neither of the two primary sensory areas in the midbrain known to be involved in orienting are a critical site of polymodal convergence. Lesions of the optic tectum abolish visual orienting while sparing tactile responsiveness; lesions of the lateral torus semicircularis abolish tactile while sparing visual responsiveness. Hence, an essential convergence, if it exists, must occur subsequent to these structures. In the course of recent studies on the organization of tectofugal pathways involved in visual orienting, we have made preliminary observations indicating that, in contrast to tectal lesions, more caudally located lesions produce visual and tactile deficits which are remarkably similar. The character of the deficits suggests a disturbance in spatial localization rather than in movement pattern. These and related findings suggest that there may be an essential convergence of visual and tactile signals in the ventral midbrain and that this convergence occurs not on the circuitry generating movement patterns but rather at an earlier processing stage in which a signal related to spatial location in some more generalized coordinate frame is created. The studies proposed here are directed primarily at confirming and extending the preliminary lesion observations. A second set of neuroanatomical studies will be undertaken to determine whether tectal and lateral toral efferents converge on common target structures. Finally, we will initiate electrophysiological studies in an effort to determine whether there is an effective convergence of visual and tactile information in a likely ventral midbrain structure, the nucleus of the medial longitudinal fasiculus.